J. Nannoplankton Res. 29 (1), 2007, pp.25-30 © 2007 International Nannoplankton AssociationISSN 1210-8049 Printed by Cambridge University Press, UK25

Umbilicosphaera jordanii Bown, 2005 from the Paleogeneof Tanzania: confirmation of generic assignment and a
Paleocene origination for the Family Calcidiscaceae
Paul R. Bown*, Tom Dunkley Jones
Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK; *p.bown@ucl.ac.uk

Jeremy R. Young
Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SE7 5BD, UK
Manuscript received 23rd January, 2007; revised manuscript accepted 21st February, 2007

Abstract Scanning electron microscope images of the recently described Paleogene coccolith Umbilicosphaera
jordanii Bown, 2005, allow detailed comparison of its structure to that of extant Umbilicosphaera. The morphological and crystallographic evidence strongly support the inclusion of U. jordanii within Umbilicosphaera, and so confirms a Paleocene origination time for the extant Family Calcidiscaceae. We also recombine the species Cyclolithus
bramlettei Hay & Towe, 1962 within Umbilicosphaera, based on similar considerations of shield morphology andcrystallography.
Keywords Umbilicosphaera, Calcidiscaceae, taxonomy, Paleogene, Kilwa Group, Tanzania
1. Introduction
Umbilicosphaera jordanii was described from the Lower
Eocene of coastal Tanzania (Bown, 2005) and is a conspicuous and common component (>5%) of much of thePaleogene Kilwa Group succession (Upper PaleoceneOligocene). The species was described using lightmicroscopy and tentatively placed in the extant genus
Umbilicosphaera, based on the overall character of itsappearance. Here, we present new scanning electron
microscope (SEM) images of U. jordanii, which allow
detailed comparison of its structure to that of extant
Umbilicosphaera, as described in detail by Young et al.
(2004). This comparison strongly supports the inclusionof U. jordanii in Umbilicosphaera, and so confirms aPaleocene origination time for the extant Family
Calcidiscaceae.
2. Methods and materials
The Kilwa Group (Cretaceous-Oligocene) of Tanzania
has been studied in core material as part of a palaeoclimate research programme, the Tanzania Drilling Project(TDP). An overview of the TDP project, describing fieldtechniques, geological setting, drilling objectives andstratigraphic results, is given in Pearson et al. (2004,2006, in prep.) and Nicholas et al. (2006), and detailed
nannofossil taxonomic inventories of the Paleogene material, based on light-microscopy, have been presented inBown (2005) and Bown & Dunkley Jones (2006).
Nannofossils were viewed in smear-slides (Bown &Young, 1998) using a Zeiss Axiophot light-microscope(LM) at x1000-1250 magnification in cross-polarised(XPL) and phase-contrast (PC) light, and on broken rocksurfaces using a JEOL Digital JSM-6480LV SEM (seeLees et al., 2004 for discussion of this technique).
Descriptive terminology follows Young et al. (1997).

3. Results
Umbilicosphaera jordanii was described from LM images
that show circular coccoliths with broad shields and wide,
open central areas (Pl.1, figs 9-13). The rim displays low
birefringence, with a bright tube-cycle crossed by diagonal extinction lines, consistent with an ultrastructure of Vunits forming the distal shield, and R-units forming theproximal shield and part of the tube. The species was tentatively assigned to the genus Umbilicosphaera, as boththe overall morphology and crystallography of the coccoliths are comparable to those of the extant species U.
foliosa, and extinct Neogene species such as U. jafari andU. rotula.
We have now imaged multiple specimens of U. jordanii in the SEM, and a representative set of images isgiven in Plate 1, together with those of extant
Umbilicosphaera species, to allow a direct comparison.
The distal shield is formed from elements joined along
near-radial sutures in their outer part, but at the shield
crest the sutures kink, at which point they often showbead-like projections (Pl.1, fig.2). Individual elements
can be directly traced from the distal shield into the tube
(e.g. Pl.1, figs 1, 4), showing that a single cycle of crystal
units forms the entire distal shield and tube, as in modern
Umbilicosphaera (Pl.1, figs 3, 5). Around the inner edgeof the distal surface, there may be an area with indistinct
sutures, (Pl.1, figs 1, 2), a feature also seen in U. foliosa(Pl.1, fig.5). Above this zone of obscure sutures, the welldeveloped flat crystal faces seen on U. jordanii are almost
certainly the {100} faces of rhombohedral calcite, as is
the case on modern Umbilicosphaera (Young et al.,2004). Closer examination reveals that the crystal edges
between these rhombohedral faces in U. jordanii show
exactly the same orientation as those in extant
Umbilicosphaera, implying that they have identical aand c-axis orientations (see annotation on Pl.1, figs 1, 3).

26

Bown, Dunkley Jones, Young

Figure 1: Stratigraphic distribution of Calcidiscaceae taxa from the Paleogene of Tanzania. Nannofossil biozonation fromMartini (1971), planktonic foraminifera biozonation from Berggren & Pearson (2005). Correlation of the two plankton biozonation schemes and time-scale are from the latter. Stratigraphic extent of TDP cores shown to the left of the diagram

The proximal shields are rather flat and, in somecases, larger than the distal shields, as also seen in U.
sibogae (Pl.1, figs 1, 3). The proximal shield elements
show strong clockwise obliquity, and there is a raised collar and narrow smoother area around the inner edge (Pl.1,fig.6). A narrow, outer proximal-shield cycle is complexly intergrown with the main proximal-shield elements(Pl.1, fig.7). These proximal-shield characters are directlycomparable to modern U. foliosa (Pl.1, fig.8) and manyother, although not all, Calcidiscaceae andCoccolithaceae.
4. Discussion
The Order Coccosphaerales (Coccolithaceae andCalcidiscaceae) form placolith coccoliths with V-unit distal shields, R-unit proximal shields and embedded protococcolith rings (Young et al., 2003). Coccolithaceae coccoliths further have a complex tube formed from R-units

in the upper part and V-units in the lower part.
Calcidiscaceae coccoliths typically comprise monocyclic
distal shields with strongly curving sutures, and proximal
shields that can be mono- or bicyclic. Umbilicosphaera isdistinguished from Calcidiscus by its wide central opening, kinked distal-shield sutures and birefringent tubecycle. While these distinctions are not particularly great,
the separation of the two genera is, nevertheless, supported by genetic analysis (Saez et al., 2003).
The morphological and crystallographic observations
presented above and in Plate 1 provide unambiguous evidence that U. jordanii possesses a structure typical of theCalcidiscaceae, that is, proximal shield and lower tube Runits, distal shield and upper tube V-units, exactly thesame chirality of elements, and the proto-coccolith ringembedded inside the tube (V/R alternation is not seen on
the proximal surface). The kinked sutures and bead-likeprojections of the distal shield, and larger, bicyclic proxi-

Umbilicosphaera jordanii...Family Calcidiscaceae

mal shields with clockwise chirality, are all features seenin the extant species U. foliosa and U. sibogae, and support the inclusion of U. jordanii within Umbilicosphaera.
We also recombine the species Cyclolithus bramlettei Hay& Towe, 1962 within Umbilicosphaera, based on similar
considerations of shield morphology and crystallography(see below and Pl.2, figs 1-4, 7-12).
Previous
palaeontologicalrecordsofUmbilicosphaera placed its origination in the Early
Neogene (e.g. zone NN2, ~22Ma, according to Young,1998), but the Tanzanian Kilwa Group occurrences
extend its fossil record by 36Ma, to at least the Late
Paleocene (Figure 1). The species U. jordanii has beenfound in the oldest Paleogene drilled by the TDP (TDPSite 19, zone NP6: Nicholas et al., 2006) and it is consistently found throughout the Paleocene to Early Oligocene.
One important test of the generic classification applied
here is whether we will be able to trace lineages from ouryoungest Oligocene representatives of U. jordanii to theMiocene U. jafari or U. rotula.
The common and consistent presence in the Kilwa
Group of other coccoliths with comparable morphologies,
for example, U. bramlettei and Hayaster perplexus (Pl.2,fig.5), has now established, beyond doubt, that theCalcidiscaceae extended into the Paleocene and were asignificant component of placolith assemblages throughout the Paleogene interval (Figure 1). There is no
stratophenetic evidence for the origin of theCalcidiscaceae, but coccolith structure and moleculargenetics both suggest they evolved from theCoccolithaceae. Since the first Coccolithaceae occur inthe Early Paleocene, it is reasonable to infer that theCalcidiscaceae originated subsequent to this, and so within the Paleocene. Other taxa that are tentatively included
within the genus Calcidiscus (see Figure 1) have yet to bestudied in detail using the SEM, but their LM images suggest affinities with the Family Calcidiscaceae. The taxonomy of Paleogene Coccolithaceae and Calcidiscaceae isin need of revision, not least since there are numerous
poorly-characterised species in the literature. We intend touse the exceptionally preserved material from the TDP torevise this group and so enhance our knowledge of coccolithophore palaeodiversity and phylogeny.
5. Systematic palaeontology
Only bibliographic references not included in PerchNielsen (1985) and Bown (1998) are included in the reference list. All sample material, slides, stubs and images
are curated in the Micropalaeontology Unit of theDepartment of Earth Sciences at UCL.
Order COCCOSPHAERALES Haeckel, 1894 emend.
Young & Bown, 1997
Family CALCIDISCACEAE Young & Bown, 1997
Hayaster perplexus (Bramlette & Riedel, 1954) Bukry,
1973

27

Pl.2, figs 5, 6. Remarks: Large, circular coccoliths with asmall number of large, triangular distal-shield elements
and a diminutive proximal shield with sutures that display
clockwise chirality and pronounced kinking towards thecentre. There is little to distinguish these Paleogene forms
from the modern species. Occurrence: Rare, Upper
Paleocene (NP9); TDP Site16B.
Umbilicosphaera bramlettei (Hay & Towe, 1962) comb.
nov.
Pl.2, figs 1-4, 7-12. Basionym: Cyclolithus bramlettei
Hay & Towe, 1962, p.500, pl.5, fig.6; pl.7, fig.2. Eclogae
Geol. Helv., 55: 497-517. Remarks: Small- to mediumsized (3.5-7.5µm), narrow, ring-shaped coccoliths, distinctly bicyclic in XPL. The two cycles are similar inwidth, and the bright inner cycle is crossed by non-axial
extinction lines. It forms distinctive cubic coccospheres,seen in the LM (Pl.2, figs 11, 12). The distal-shield elements are strongly kinked, and show distinctly steppededges across the outer half of the shield, but straight edges
across the inner half, a feature identical to the extant
species U. sibogae. The proximal shield elements show
strongly clockwise obliquity and are kinked near the inneredge. Differentiation: Similar to Coronocyclus nitescens
in LM appearance, but has a more clearly defined, brighttube-cycle in XPL and lacks the characteristic serrated
outline. Coronocyclus also appears to have significantly
modified placolith structure, unlike typical calcidiscids.
Comparable to U. jordanii and Calcidiscus? protoannulus, but the two rim-cycles are similar in width and thetube-cycle details are distinct, being more clearly defined
than the former, and crossed by straighter, more diagonal
extinction lines than the latter. Occurrence: Upper
Paleocene to Lower Oligocene (NP6-21); TDP Sites 2-4,7A, 7B, 8, 10-14, 16-19.
Umbilicosphaera jordanii Bown, 1985
Pl.1, figs 1, 2, 4, 6, 7, 9-13. Remarks: The distal-shieldsutures are distinctly kinked and, like the modern speciesof Umbilicosphaera, this may be explained by relatively
simple, single crystal-units whose surfaces interact
obliquely with the sloping shield surface (Young &Henriksen, 2003; Young et al., 2004). The proximal
shields are relatively large and flat, as in U. sibogae,
where this feature is related to large coccosphere size. For
further ultrastructural detail, see above. Occurrence:
Upper Paleocene to Oligocene (NP6-23); TDP Sites 1, 3,7A, 7B, 8, 10-14, 16-19. Common in the Late PaleoceneEarly Eocene, and Late Eocene-Early Oligocene, but may
be rarer or absent in parts of the Middle Eocene.
Acknowledgements
Thanks to the Tanzania Drilling Project team, and also theNatural Environment Research Council, Tanzania Petroleum
Development Corporation and UCL Graduate School, who haveprovided resources and funding. Good electron microscopy isdependent upon excellent technical support, and we thank Alex
Ball at the NHM and Jim Davy at UCL. We are also apprecia-

28Bown, Dunkley Jones, Youngtive of the reviews provided by Drs Ric Jordan and MarkusGeisen.

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Cited taxa
Calcidiscaceae Young & Bown, 1997
Calcidiscus Kamptner, 1950
Calcidiscus? bicircus Bown, 2005
Calcidiscus? gerrardii Bown, 2005
Calcidiscus? henrikseniae Bown, 2005
Calcidiscus? parvicrucis Bown, 2005
Calcidiscus? protoannulus (Gartner, 1971) Loeblich & Tappan,
1978
Coccolithaceae Poche, 1913 emend. Young & Bown, 1997
Coccosphaerales Haeckel, 1894 emend. Young & Bown, 1997
Coronocyclus nitescens (Kamptner, 1963) Bramlette &Wilcoxon, 1967 [probably a junior synonym of prinion(Deflandre & Fert, 1954)]
Hayaster Bukry, 1973
Hayaster perplexus (Bramlette & Riedel, 1954) Bukry, 1973
Hayella simplex Bown & Dunkley Jones, 2006
Hayella situliformis Garter, 1969
Umbilicosphaera Lohmann, 1902
Umbilicosphaera anulus (Lecal, 1967) Young & Geisen in
Young et al., 2003
Umbilicosphaera bramlettei (Hay & Towe, 1962) comb. nov.
Umbilicosphaera foliosa (Kamptner, 1963 ex Kleijne, 1993)
Geisen in Sáez et al., 2003
Umbilicosphaera jafari Müller, 1974
Umbilicosphaera jordanii Bown, 2005
Umbilicosphaera rotula (Kamptner, 1956) Varol, 1982
Umbilicosphaera sibogae (Weber-van Bosse, 1901) Gaarder,1970

Umbilicosphaera jordanii...Family Calcidiscaceae

Plate 1Comparison of U. jordanii with modern U. foliosa and U. sibogae
Black annotation lines on 1 and 3 trace crystal edges representing edges of the {100} faces ofrhombohedral calcite
Ages of specimens given in bottom right corner
Scale-bars = 1µm

2930Bown, Dunkley Jones, YoungPlate 2U. bramlettei, Hayaster perplexus and other Umbilicosphaera spp.
Ages of specimens given in bottom right corner
Scale-bars = 1µm